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First Dark Matter Search with Nuclear Recoils from the XENONnT Experiment
No full textInternational audienceWe report on the first search for nuclear recoils from dark matter in the form of weakly interacting massive particles (WIMPs) with the XENONnT experiment which is based on a two-phase time projection chamber with a sensitive liquid xenon mass of ~t. During the approximately 1.1 tonne-year exposure used for this search, the intrinsic Kr and Rn concentrations in the liquid target were reduced to unprecedentedly low levels, giving an electronic recoil background rate of in the region of interest. A blind analysis of nuclear recoil events with energies between ~keV and ~keV finds no significant excess. This leads to a minimum upper limit on the spin-independent WIMP-nucleon cross section of for a WIMP mass of at confidence level. Limits for spin-dependent interactions are also provided. Both the limit and the sensitivity for the full range of WIMP masses analyzed here improve on previous results obtained with the XENON1T experiment for the same exposure
Search for events in XENON1T associated with Gravitational Waves
No full textInternational audienceWe perform a blind search for particle signals in the XENON1T dark matter detector that occur close in time to gravitational wave signals in the LIGO and Virgo observatories. No particle signal is observed in the nuclear recoil, electronic recoil, CENS, and S2-only channels within 500 seconds of observations of the gravitational wave signals GW170104, GW170729, GW170817, GW170818, and GW170823. We use this null result to constrain mono-energetic neutrinos and Beyond Standard Model particles emitted in the closest coalescence GW170817, a binary neutron star merger. We set new upper limits on the fluence (time-integrated flux) of coincident neutrinos down to 17 keV at 90% confidence level. Furthermore, we constrain the product of coincident fluence and cross section of Beyond Standard Model particles to be less than cm/cm in the [5.5-210] keV energy range at 90% confidence level
Preclinical irradiations at conventional and very high dose rates (FLASH-RT) on small animals at the ARRONAX research cyclotron: repositioning, margins and field sizes
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Measurement of the production of charm jets tagged with D mesons in pp collisions at = 5.02 and 13 TeV
No full textInternational audienceThe measurement of the production of charm jets, identified by the presence of a D meson in the jet constituents, is presented in proton–proton collisions at centre-of-mass energies of = 5.02 and 13 TeV with the ALICE detector at the CERN LHC. The D mesons were reconstructed from their hadronic decay D → Kπ and the respective charge conjugate. Jets were reconstructed from D-meson candidates and charged particles using the anti-k algorithm, in the jet transverse momentum range 5 < p< 50 GeV/c, pseudorapidity |η| < 0.9 − R, and with the jet resolution parameters R = 0.2, 0.4, 0.6. The distribution of the jet momentum fraction carried by a D meson along the jet axis was measured in the range 0.4 << 1.0 in four ranges of the jet transverse momentum. Comparisons of results for different collision energies and jet resolution parameters are also presented. The measurements are compared to predictions from Monte Carlo event generators based on leading-order and next-to-leading-order perturbative quantum chromodynamics calculations. A generally good description of the main features of the data is obtained in spite of a few discrepancies at low p. Measurements were also done for R = 0.3 at = 5.02 and are shown along with their comparisons to theoretical predictions in an appendix to this paper.[graphic not available: see fulltext
Detector signal characterization with a Bayesian network in XENONnT
No full textInternational audienceWe developed a detector signal characterization model based on a Bayesian network trained on the waveform attributes generated by a dual-phase xenon time projection chamber. By performing inference on the model, we produced a quantitative metric of signal characterization and demonstrate that this metric can be used to determine whether a detector signal is sourced from a scintillation or an ionization process. We describe the method and its performance on electronic-recoil (ER) data taken during the first science run of the XENONnT dark matter experiment. We demonstrate the first use of a Bayesian network in a waveform-based analysis of detector signals. This method resulted in a 3% increase in ER event selection efficiency with a simultaneously effective rejection of events outside of the region of interest. The findings of this analysis are consistent with the previous analysis from XENONnT, namely a background-only fit of the ER data
Fate of critical fluctuations in an interacting hadronic medium using maximum entropy distributions
No full textInternational audienceWe study the evolution of critical fluctuations in an expanding system within a hadronic transport approach. The initialization of the system with critical fluctuations is achieved by coupling the ideal hadron resonance gas cumulants to the ones from the 3d Ising model and generating the net and total particle number distribution from the principle of maximum entropy. These distributions are then evolved using realistic hadronic interactions. We systematically investigate the evolution of the critical fluctuations initialized at various temperatures and chemical potentials along a freeze-out line. We find that resonance regeneration and isospin randomization processes have the strongest influence on the evolution of the fluctuations. Additionally, the sets of particles coupled to the critical mode are modified to assess the strength of the propagation of correlations through interactions. We find that in the scaling region of the critical point correlations are propagated through the whole collisional history and are still present after the kinetic freeze-out of the matter if the coupling strength is large enough
Measurement of the hyperon lifetime
No full textInternational audienceA new, more precise measurement of the hyperon lifetime is performed using a large data sample of PbPb collisions at TeV with ALICE. The and hyperons are reconstructed at midrapidity using their two-body weak decay channel and . The measured value of the lifetime is . The relative difference between the lifetime of and , which represents an important test of CPT invariance in the strangeness sector, is also measured. The obtained value is consistent with zero within the uncertainties. Both measurements of the hyperon lifetime and of the relative difference between and are in agreement with the corresponding world averages of the Particle Data Group and about a factor of three more precise
Elliptic flow of charged particles at midrapidity relative to the spectator plane in Pb–Pb and Xe–Xe collisions
No full textInternational audienceMeasurements of the elliptic flow coefficient relative to the collision plane defined by the spectator neutrons v2{ΨSP} in collisions of Pb ions at center-of-mass energy per nucleon–nucleon pair sNN=2.76 TeV and Xe ions at sNN=5.44 TeV are reported. The results are presented for charged particles produced at midrapidity as a function of centrality and transverse momentum for the 5–70% and 0.2–6 GeV/c ranges, respectively. The ratio between v2{ΨSP} and the elliptic flow coefficient relative to the participant plane v2{4}, estimated using four-particle correlations, deviates by up to 20% from unity depending on centrality. This observation differs strongly from the magnitude of the corresponding eccentricity ratios predicted by the TRENTo and the elliptic power models of initial state fluctuations that are tuned to describe the participant plane anisotropies. The differences can be interpreted as a decorrelation of the neutron spectator plane and the reaction plane because of fragmentation of the remnants from the colliding nuclei, which points to an incompleteness of current models describing the initial state fluctuations. A significant transverse momentum dependence of the ratio v2{ΨSP}/v2{4} is observed in all but the most central collisions, which may help to understand whether momentum anisotropies at low and intermediate transverse momentum have a common origin in initial state fluctuations. The ratios of v2{ΨSP} and v2{4} to the corresponding initial state eccentricities for Xe–Xe and Pb–Pb collisions at similar initial entropy density show a difference of (7.0±0.9)% with an additional variation of +1.8% when including RHIC data in the TRENTo parameter extraction. These observations provide new experimental constraints for viscous effects in the hydrodynamic modeling of the expanding quark–gluon plasma produced in heavy-ion collisions at the LHC
Production of , (), and in jets and in the underlying event in pp and pPb collisions
No full textInternational audienceThe production of strange hadrons (, Λ, Ξ, and Ω), baryon-to-meson ratios (Λ/, Ξ/, and Ω/), and baryon-to-baryon ratios (Ξ/Λ, Ω/Λ, and Ω/Ξ) associated with jets and the underlying event were measured as a function of transverse momentum (p) in pp collisions at = 13 TeV and p Pb collisions at = 5.02 TeV with the ALICE detector at the LHC. The inclusive production of the same particle species and the corresponding ratios are also reported. The production of multi-strange hadrons, Ξ and Ω, and their associated particle ratios in jets and in the underlying event are measured for the first time. In both pp and p–Pb collisions, the baryon-to-meson and baryon-to-baryon yield ratios measured in jets differ from the inclusive particle production for low and intermediate hadron p (0.6–6 GeV/c). Ratios measured in the underlying event are in turn similar to those measured for inclusive particle production. In pp collisions, the particle production in jets is compared with Pythia 8 predictions with three colour-reconnection implementation modes. None of them fully reproduces the data in the measured hadron p region. The maximum deviation is observed for Ξ and Ω which reaches a factor of about six. The event multiplicity dependence is further investigated in p−Pb collisions. In contrast to what is observed in the underlying event, there is no significant event-multiplicity dependence for particle production in jets. The presented measurements provide novel constraints on hadronisation and its Monte Carlo description. In particular, they demonstrate that the fragmentation of jets alone is insufficient to describe the strange and multi-strange particle production in hadronic collisions at LHC energies.[graphic not available: see fulltext